When her son's persistent cough worsened into asthma as heavy, toxic smog plagued Beijing for days on end, Huang Liwen decided that she had had enough.

The vice-president of marketing at an aircraft leasing firm, who moved from California to Beijing in early 2012, was about to put in a request to relocate when her firm announced that it was moving its Asia-Pacific office to Singapore.

"We made the decision to move out of Beijing without any hesitation," she told The Straits Times. "It's a great city but unfortunately the air quality is too bad to raise a family there."

Many others like Huang have similarly upped and left China, turned down job opportunities there or moved to cities like Shanghai which has cleaner air as concerns over the negative health effects of smog dim the allure of working in the capital of the world's No. 2 economy.

Chris Watkins, managing partner of Beijing-based head- hunting firm Cornerstone Global Partners, told The Straits Times that while there has not been a mass exodus as yet, convincing senior executives to relocate to Beijing from places like Singapore, Hong Kong and Shanghai has been increasingly difficult.

"There has been so much media attention on the pollution problem over the last 12 to 18 months. But the pollution has always been here, so I think last January was a tipping point where the media really put the big push on the story," he said.

"I also think locals are much more vocal about the issue since quality of life has become increasingly important in addition to career advancement."

World Health Organisation director-general Margaret Chan said in a March interview with Bloomberg TV: "Talented people have actually talked to me, and they've changed their decision to settle in China because of the air pollution. I think the Chinese authorities understand this and they know what's going on."

Britain-based lawyer Linda Zhang, 25, turned down a two-year stint in her firm's Beijing office despite the overseas work experience that would benefit her resume. "I'm still interested in working in Asia but would much prefer working in cities like Tokyo, Seoul or Shanghai, where the quality of life is better," she said. "I don't want to worry constantly about my health."

Experts say concerns that the severity of China's pollution might be sapping the country's talent, and hence, competitiveness, have surfaced. Smog also undermines China's aim of attracting overseas talent - as many as two million people in all - from 2011 to 2015 to work in the mainland as part of the development drive.

A recent report by the American Chamber of Commerce in Beijing found that almost half of the 365 foreign firms surveyed said concerns over air quality were turning senior executives away.

Pollution is "a difficulty in recruiting and retaining senior executive talent", said the report, which covers businesses in China's northern cities. The 2014 figure is up from 19 per cent of foreign firms that said smog was a problem for recruitment in 2010.

These figures offer some of the strongest evidence yet on how pollution is hurting recruitment despite Premier Li Keqiang's pledge to "declare war" on pollution at the opening of the annual Parliament session last month.

John Sung, operations director at recruitment consultancy Kelly Services China, said China continues to face talent shortage. "Having a stagnant talent pool or a reduction will obviously negatively affect the global competitiveness of Beijing in the long run. However... there has not be a sizeable outflow of talent nor significant reduction in newcomers to severely impact Beijing's competitiveness at this stage."

But some foreign executives are already using pollution as a bargaining chip to negotiate higher salary packages, particularly those asked to relocate to Beijing, Sung said. Japan's Panasonic, for instance, has also said it will give employees sent to China a wage premium in the light of the hazardous air pollution, a possible first for an international firm.

Yet for many, compensation remains secondary to health with others even enduring inconveniences just to live smog-free.

Huang said: "My customers are all in China and it's definitely inconvenient for me to travel a lot but it's worth it for my family to live in fresh air."